Robert lundell



(No Model.)

R. LUNDELL.

DYNAMO ELECTRIC MACHINE.

No. 571,310. Patented Nov. 10, 1896.

UNITED STATES PATENT OFFICE.

ROBERT LUNDELL, OF BROOKLYN, NEW YORK, ASSIGNOR OF 'lWVO-TIIIRDS TOEDWARD ll. JOHNSON, OF NEXY YORK, N. Y.

DYNAMO-ELECTRlC MACHINE.

SPECIFICATION forming part of Letters Patent No. 571,310, dated November10, 1896.

Application filed October '7, 1895. Serial No. 564,847. (No model.)

To (LU whom it ma 1 concern/.-

3e it known that I, ROBERT LUNDELL, a citizen of the United States,residing at Brooklyn, in the county of Kings and State of New York, 5have made a new and useful invention in Dynamo-Electric Machines, ofwhich the follow-- ing is a specification.

Myinvention is directed particularly to improvements in direct-currentdynamo-elecro tric machines, and its object is to prevent the shiftingor distortion of the magnetic fluid in machines of this type whenworking under full load.

It is well known by those skilled in the art of designing and using suchdynamo-electric machines that the ampere-turns due to thearniature-currents have a demagnetizing and cross-magnetizing effectupon the fieldpoles thereof. In other words, the armature ampere-turnswhich lie between the double angle of lead have a demagnetizing effectupon the magnetic circuits and the armature ampere-turns which liedirectly under the poles have a cross-magnetizing effect or a tendencyto weaken the pole strength at that pole corner where the commutationtakes place and to increase the pole strength at the opposite polecorner. This demaguetizing effect can readily be compensated for bycompounding, but the cross-maguetizing or distorting effect is not soeasily overcome. Various methods have heretofore been suggested by thoseskilled in the art for overcoming this objectionable feature, and thepresent invention 3 5 is directed to a simple method of and means foraccomplishing this object.

My invention will be fully understood by referring to the accompanyingdrawings, in which Figure 1 illustrates in side elevational view awell-known form of compound-wound four pole dynamo-electric machineembodying my improvement in the structure of the field polepieces. Fig.2 is an end view of one of the 4 5 field-magnet coils and myimprovedfield-magnet poles surrounded thereby. Fig. 3 is an enlarged sectionalview taken on the line Fig. 2, a diagrammatic view of various magneticconditions being also illustrated in full and dotted lines at the top ofsaid figure.

l of l).

A represents the armature of the machine, which in this instance isdesigned to rotate from left to right.

M represents the field-magnet coils of a well-known form ofcompound-won11d field.

The comm utator-brushes, four in number, are represented by the letters0, I, O and C, Fig. 1.

The field-magnet poles, or rather the fieldmagnet cores, are divided, asshown, into two distinct parts a and Z), practicallyof the same crosssection. The pole-face of the part a has an area only slightly largerthan a crosssection of said part, whereas the pole-face of the part Z)has an area of at least twice the same cross-section. The part Z), aswill be observed, is provided with a wedge-shaped polar projection 21,extending laterally from the dotted line ,2 2', (shown in Figs. 2 and3,) and is so proportioned that it covers about the same area as thepole-face of the part (1, its thickest part, having a cross-section atits base on the section-line 42' about equal to one-half of thecross-section of 7).

The material used for the iield-n1agnet cores is cast-steel, althoughthese cores mayin some instances be constructed of sheet-iron punchings. The induction across the air-gap is such that the field-core b issaturated when the machine is working under a light load and Sosupersaturated at full load. For example, if at light load the inductionacross the air-gap is seven thousand five hundred centimetergram-seconds lines per square centimeter under the field-magnet core aand seven thousand per square centimeter under the fieldmagnet-core b itwill be seen that the induc tion in b is about twice as high as in a. Inother words, I) is saturated, whereas a is far below saturation andcapable of increasing 0 the induction under its pole-face as the magnetizing force from the compound winding increases with the load.

At full load the magnetizing force upon the magnetic circuit through ais as follows: 5 shunt ampere-turns series ampere-turns on fieldcoresarmature ampere-turns between the double angle of lead the armatureampere-turns that lie under the pole-face The sum of these forces issuch that the induction under the pole-face of a has increased by apredetermined amount. (See Fig. 3.)

The magnetizing forces acting upon the magnetic circuit through I) atfull load are as follows: shunt am pore-turns series ampereturns on thefield-coils armature ampereturns between the double angle of lead thearmature ampere-turns that lie' under the poleface of the part a. Thesum of these magnetic forces, although considerably greater than thoseacting upon the circuit through the part a, are unable to materiallyincrease the induction from the pole-face of the part b on account ofthe high saturation of said part and its extended polar projection 13.The inductive effect across the air-gap is represented diagrammaticallyin Fig. 3 by the heavy line A A A at no load and the heavy line A A A atfull load. The fine line B B 13 represents diagrammatically thecross-magnetizing effect of the armature, and the dotted line A A Aparallel therewith, the resultant inductive effect across the air-gap atfull load of a machine which is provided with solid pole-pieces ofwell-known form. This method of representing the inductive effects ofthe field-magnets diagrammatically by an irregular line A A A and thecross-magnet izing effects of the-armature by a fine diagonal line l5 l3and the resultant effect thereof by a dotted parallel diagonal line A AA is fully explained in Volume 2 of Practical Electrical Eng meering, apublication published by Biggs 86 00., of Nos. 139 and M0 SalisburyOourt, Fleet Street, E. 0., London, England, and edited by Gisbert Knappand other well-known electrical engineers, and reference is had tochapter XI, pp. 72 to 81, of said publication for the full explanationthereof.

The effect of my peculiar form of fieldmagnet pole with the polarprojection 27 is illustrated upon this diagram by the full irregularline A A A, thereby showing that the magnetic fringe or line ofcommutation between no lead A A A and full load A A A varies but little.In other words, this diagram shows that with a field-magnet pole ofwell-known solid form of construction the magnetic fringe or line ofcommutation shifts between no load and full load to such an extent thata shifting of the commutator-brushes is required, while with myimprovement this shifting of the line of commutation or magnetic fringeis scarcely appreciable, the mag netic effect of the polar projection 19being such that the brushes may be allowed to remain constantly in oneposition for all loads.

If it should be required to run the generator in the opposite direction,it would of course in that event be necessary to reverse the directionof the field cores or poles.

I do not limit myself to the special structural arrangement herein shownand described for effecting the result sought, as I believe it isbroadly new with me to increase the magnetic effect of adynamo-electricmachine in that portion of the magnetic field wherein thebrushes are located by increasing the magnetic reluctance of thefield-cores or pole-pieces thereof in the direction of rotation of thearmature or rotary part in proportion to the work which the machine iscalled upon to perform and without the use of auxiliary coils and toutilize this effect for the prevention of sparking at the brushes, andmy claims hereinafter made are therefore to be construed as of the mostgeneric nature.

Having thus described my invention, what I claim, and desire to secureby Letters Pat ent of the United States, is-

1. A dynamo-electric machine having its field cores or poles arrangedwith saturated and unsaturated portions as and for the pur posedescribed.

2. A dynamo-electric machine having fieldmagnet cores or pole-pieces sodivided and arranged that there is an increase in the magneticreluctance in the direction of rotation of the armature or rotary part.

2-3. A dynamo-electric machine having fieldmagnet cores and pole-piecesso divided and arranged that the magnetic reluctance is caused toincrease in the direction of rotation of the armature or rotary part.

Means for preventing the shifting of the magnetic field with increasingload in a dynamo-electric machine, consisting of fieldcores orpole-pieces having low magnetic reluctance on the side where commutationtakes place and high magnetic reluctance on the opposite side of thepole while the armature or rotary part rotates from the pole of lowmagnetic reluctance toward the pole of high magnetic reluctance.

5. I11 a dynamo-electric machine a field magnet coil surrounding afield-magnet pole which is divided into two parts separated by anair-space, one of said parts having an inner field-pole surface ofgreater area than the other.

(3. In a dynamo-electric machine a fieldmagnet coil surrounding twofield-magnet poles separated from each other by an interveningair-space, one of said fieldnnagnet poles having a wedge-shapedpole-piece, the inner face of which is of greater area than the innerface of the other pole-piece, sul stantially as described.

In testimony whereof I have hereunto subscribed my name this 5th day ofOctober, 1895.

ROBERT LUNDELL.

Witnesses:

O. J. Knvrunn, M. M. ROBINSON.

IIO

